1. Field of the Invention
This invention relates to solid electrolytic capacitors using an anode made of a valve metal or an alloy thereof.
2. Description of Related Arts
Tantalum solid electrolytic capacitors using a sintered tantalum powder body as an anode contain an oxide having a dielectric constant approximately twice larger than that of aluminum oxide and therefore can achieve high capacitance. For this reason, tantalum solid electrolytic capacitors have recently been used in a wide range of fields including cellular phones and personal computers.
Nevertheless, even higher capacitance has been demanded. Niobium has attracted much attention as an alternative anode material to tantalum. Oxides of niobium have dielectric constants approximately 1.8 times larger than that of tantalum oxide. Therefore, consideration has been given to the development of solid electrolytic capacitors using niobium for an anode (see, for example, Published Japanese Patent Application No. H11-329902).
However, if niobium is used for an anode, there arises a problem of high leakage current. In view of this problem, there is a demand for solid electrolytic capacitors capable of reducing the leakage current.